1. Field of the Invention
The present invention relates to a semiconductor device fabricated by using an SOI (Silicon on Insulator) substrate and a method of fabricating the same. Specifically, the invention relates to a semiconductor device including a thin film transistor (hereinafter referred to as TFT) formed on a SOI substrate.
Incidentally, in the present specification, the term semiconductor device indicates any device capable of functioning by using semiconductor characteristics. Thus, the semiconductor device includes not only a TFT but also an electro-optical device typified by a liquid crystal display device or a photoelectric conversion device, a semiconductor circuit in which TFTs are integrated, and electronic equipment containing such an electro-optical device or semiconductor circuit as a part.
2. Description of the Related Art
In recent years, there have been remarkable developments in VLSI techniques, and particular attention has been paid to a SOI (Silicon on Insulator) structure for achieving low power consumption. In this technique, an active region (channel formation region) of a FET, which has been conventionally formed of bulk single crystal silicon, is made a thin film single crystal silicon.
In a SOI substrate, a buried oxide film made of silicon oxide exists on single crystal silicon, and a single crystal silicon thin film is formed thereon. Various methods for fabricating such SOI substrates are known. As a typical SOI substrate, a SIMOX substrate is known. The term SIMOX is an abbreviation for Separation-by-Implanted Oxygen, and oxygen is ion implanted into a single crystal silicon substrate to form a buried oxide layer. The details of the SIMOX substrate are disclosed in K. Izumi, M. Docken and H. Ariyoshi: xe2x80x9cC.M.O.S. devices fabrication on buried SiO2 layers formed by oxygen implantation into siliconxe2x80x9d, Electron. Lett., 14, 593-594 (1978).
Recently, attention has also been paid to a bonded SOI substrate. The bonded SOI substrate achieves the SOI structure by bonding two silicon substrates as suggested by its name. If this technique is used, a single crystal silicon thin film can be formed also on a ceramic substrate or the like.
Among the bonded SOI substrates, in recent years, attention has been especially paid to a technique called ELTRAN (registered trademark by Canon K.K.). This technique is a method of fabricating a SOI substrate using selective etching of a porous silicon layer. The particular technique of the ELTRAN method is disclosed in, K. Sakaguchi et al., xe2x80x9cCurrent Progress in Epitaxial Layer transfer (ELTRAN)xe2x80x9d, IEICE TRANS. ELECTRON. Vol. E80 C. No. 3 pp. 378-387 March 1997, in detail.
Another SOI technique attracting attention, there is called Smart-Cut (registered trademark of SOITEC Co.). The Smart-Cut method is a technique developed by SOITEC Co. in France in 1996, and is a method of fabricating a bonded SOI substrate using hydrogen embrittlement. The particular technique of the Smart-Cut method is disclosed in detail xe2x80x9cIndustrial Research Society (Kogyo Chosa Kai); Electronic Material, August, pp. 83-87, 1977xe2x80x9d.
When the foregoing SOI substrate is fabricated, a single crystal silicon substrate having a main surface of a crystal face of a {100} plane (crystal orientation is  less than 100 greater than  orientation) has been used in all of these techniques. The reason is that the {100} plane has lowest interface state density (Qss) and is suitable for a field effect transistor that is sensitive to interface characteristics.
However, with respect to the SOI substrate used for a TFT, since a single crystal silicon thin film must be formed on an insulating layer, higher priority must be given to the adhesion to the insulating layer than the interface state density. That is, even if the interface state density is low, it is meaningless if the single crystal silicon thin film peels off.
The present invention was conceived in view of such problems, and an object thereof is to provide a semiconductor device with high reliability by fabricating a SOI substrate suitable for a TFT and by forming TFTs on the substrate.
The structure of the present invention disclosed in the present specification is fabricated by a method comprising the steps of:
forming a hydrogen-containing layer at a predetermined depth in a single crystal semiconductor substrate having a main surface of a {110} plane;
bonding the single crystal semiconductor substrate and a supporting substrate to each other;
splitting the single crystal semiconductor substrate by a first heat treatment along the hydrogen-containing layer;
performing a second heat treatment at a temperature of 900 to 1200xc2x0 C.;
grinding a single crystal semiconductor layer remaining on the supporting substrate and having a main surface of a {110} plane; and
forming a plurality of TFTs each having an active layer in the single crystal semiconductor layer.
Further, another structure of the present invention is fabricated by a method comprising the steps of:
forming a porous semiconductor layer by anodization of a single crystal semiconductor substrate having a main surface of a {110} plane;
performing a heat treatment on the porous semiconductor layer in a reducing atmosphere;
carrying out epitaxial growth of a single crystal semiconductor layer having a main surface of a {110} plane on the porous semiconductor layer;
bonding the single crystal semiconductor substrate and a supporting substrate to each other;
performing a heat treatment at a temperature of 900 to 1200xc2x0 C.;
grinding the single crystal semiconductor substrate until the porous semiconductor layer is exposed;
removing the porous semiconductor layer to expose the single crystal semiconductor layer; and
forming a plurality of TFTs each having an active layer of the single crystal semiconductor layer on the supporting substrate.
Still, another structure of the present invention is fabricated by a method comprising the steps of:
forming an oxygen-containing layer at a predetermined depth in a single crystal semiconductor substrate having a main surface of a {110} plane;
changing the oxygen-containing layer into a buried insulating layer by a heat treatment; and
forming a plurality of TFTs each having an active layer of a single crystal semiconductor layer having a main surface of a {110} plane on the buried insulating layer.